Compound airfoil

ABSTRACT

An airfoil is provided that has an arrangement that improves the lift of an airfoil and that include surface features that change the performance of the airfoil. Protrusions are provided on the top surface of the airfoil such that channels are formed between adjacent protrusions that affect the flow of air there through. In an additional respect, indentations can be provided on the bottom surface of the airfoil that affect the flow of air there through.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of U.S.Patent Application No. 61/534,236, filed Sep. 13, 2011 which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to airfoils, and, more particularly,enhancement of normal airfoils by incorporating venturi and diffusers toincrease airfoil effectiveness.

BACKGROUND OF THE INVENTION

An airfoil is a member that has a shape such that when it is movedthrough a fluid (e.g., air or water) an aerodynamic force (e.g. lift anddrag) is produced. Common airfoils include the wing of an airplane, awind turbine, helicopter rotor blade, or turbine blade for a gas turbineor jet engine, airplane propeller or the sail of a sailboat, forexample.

The force or lift produced by an airfoil is primarily a result of thefluid velocity, angle of attack, and the shape of the airfoil. However,other modification to the airfoil may increase the lift. For example,U.S. Patent No. 2,427,972 to Melehior et al., discusses the creation ofventuri that are formed via a slot that extends between the upper andlower surfaces of the airfoil. This design, however, relies on directingair flow through the body of the airfoil. The present invention providesfundamental improvements over this design and others.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an airfoil is provided thatincludes a top surface extending between a leading edge and a trailingedge on a top side of the airfoil and defining a chord lengththerebetween. A bottom surface extends between the leading edge and thetrailing edge on a bottom side of the airfoil. A plurality ofprotrusions are on the top surface of the air foil. Two adjacentprotrusions define a channel therebetween that extends in the directionof the chord length of the airfoil. Each channel has a leading portion,a middle portion, and a trailing portion. The channel is sized andshaped such that the leading portion and the trailing portion are widerthan the middle portion.

In a further aspect, each channel extends along a majority of the topsurface in the direction of the chord length.

In yet a further aspect, the length of the leading portion of eachchannel is shorter than the middle portion in the direction of the chordlength.

In a still further aspect, the length of the trailing portion of eachchannel is longer than the middle portion in the direction of the chordlength.

In further aspect, each channel extends along less than half of the topsurface in the direction of the chord length.

In yet another further aspect, the walls of adjacent protrusionsconverge along a curved trajectory to define the leading portion of eachchannel.

In another further aspect, the walls of adjacent protrusions divergealong a generally linear trajectory to define the trailing portion ofeach channel.

In a further aspect, the walls of adjacent protrusions extend generallyparallel to each other to define the middle portion of each channel.

In yet a further aspect, the distance between a top surface of eachprotrusion and the top surface of the airfoil defines a depth of eachchannel, and the depth of each channel is greater in the leading portionthan the middle portion and the trailing portion.

In a still further aspect, each protrusion extends around the leadingedge to the bottom surface of the airfoil such that adjacent protrusionsform channels on the bottom surface of the airfoil.

According to another aspect, an airfoil is provided that has a topsurface extending between a leading edge and a trailing edge on a topside of the airfoil and defines a chord length therebetween. A bottomsurface extends between the leading edge and the trailing edge on abottom side of the airfoil. A plurality of indentations on the bottomsurface of the air foil are provided that define a channel. Eachindentation has a leading portion and a trailing portion. The channel issized and shaped such that the trailing portion is wider than theleading portion.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a graph illustrating the aerodynamic performance of an airfoilshowing most of the pressure differential and lift being creating in theforward part of the airfoil;

FIG. 2 is a top plan view on an airfoil with a venturi according to anembodiment of the invention;

FIG. 3 is an isometric view on an airfoil having multiple venturi ofFIG. 2;

FIG. 4 is a top plan view on an airfoil with a venturi according to asecond embodiment of the invention;

FIG. 5 is an isometric view on an airfoil having multiple venturi ofFIG. 4;

FIG. 6 is a top plan view on an airfoil with a venturi according to athird embodiment of the invention;

FIG. 7 is an isometric view on an airfoil having multiple venturi ofFIG. 6;

FIG. 8 is a top plan view on an airfoil with a venturi according to afourth embodiment of the invention;

FIG. 9 is an isometric view on an airfoil having multiple venturi ofFIG. 8;

FIG. 10 is a top plan view on an airfoil with a venturi according to afifth embodiment of the invention;

FIG. 11 is an isometric view on an airfoil having multiple venturi ofFIG. 10;

FIG. 12 is a cross-section view on an airfoil with venturi profiles ofdiffering depths according further embodiments of the invention;

FIGS. 13 and 14 are isometric views of airfoils having multiple venturiof FIG. 12;

FIGS. 15 and 16 are isometric views of airfoils having multiple venturiat different spacings;

FIGS. 17 and 18 are views of an airfoil having multiple venturi of afirst profile;

FIGS. 19 and 20 are views of an airfoil having multiple venturi of asecond profile;

FIGS. 21 and 22 are views of an airfoil having multiple venturi of athird profile;

FIGS. 23-25 are views of an airfoil having multiple venturi of a fourthprofile;

FIGS. 26 and 27 are views of an airfoil having multiple venturi of afifth profile;

FIGS. 28-31 are views of an airfoil having multiple venturi of a sixthprofile;

FIG. 32 is an exemplary schematic of an airfoil that corresponds to theairfoil illustrated in FIGS. 19 and 20;

FIG. 33 is an exemplary schematic of an airfoil that corresponds to theairfoil illustrated in FIGS. 21 and 22;

FIG. 34 is an exemplary schematic of an airfoil that corresponds to theairfoil illustrated in FIGS. 19 and 20;

FIG. 35 is an exemplary schematic of an airfoil that corresponds to theairfoil illustrated in FIGS. 26 and 27;

FIG. 36 is an exemplary schematic of an airfoil that corresponds to theairfoil illustrated in FIGS. 17 and 18;

FIGS. 37 and 38 is an exemplary schematic of an airfoil that correspondsto the airfoil illustrated in FIGS. 23-25; and

FIG. 39 is an exemplary schematic of an airfoil that corresponds to theairfoil illustrated in FIGS. 28-31.

DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

By way of overview and introduction, the present invention provides anarrangement that improves the lift of an airfoil. The structuresdescribed herein relate to airfoils that include surface features thatchange the performance of the airfoil. The various arrangementsdescribed herein impart a modification of the airflow around theairfoil. Various structures of differing sizes and shapes provideenhanced lift and aerodynamic characteristics to an airfoil by adding avertical element to airfoils to increase airflow velocity over the topof the wing thereby reducing static pressure and increasing lift. Thediffuser aspect of this invention reduces airflow velocity on theunderside of the wing thereby increasing static pressure and increasinglift. The figures included herein illustrate airfoils that includeventuri on the upper surface of an airfoil. The various figures showventuri of different sizes, shapes, and profiles and at differentpositions and spacing along the airfoil. The figures included herein aremerely illustrative embodiments and venturi having differentcombinations and variations of the sizes, shapes, profiles, positionsand spacing can be made without departing from the invention.

FIGS. 2 and 3 illustrate an airfoil 10 that includes venturi 12. Anairfoil having a base shape corresponding to National Advisory Committeefor Aeronautics (NACA) airfoil shape designated NACA 0015 was selectedas the base airfoil shape. The base shape of the airfoil was selectedbased on whether the airfoil undergoes trailing edge stall. An airfoilthat undergoes trailing edge stall is preferred because 1) a leadingedge separation bubble could disrupt the flow into the venturi, and 2)the stream wise vortices created by the venturi will only help suppressstall on the trailing edge. Accordingly, other shape airfoils arecontemplated and the invention is not limited to a particular airfoilshape. FIG. 1 shows a typical pressure distribution for a NACA 0015airfoil at a 10° angle of attack. Cp is the pressure coefficient, andx/c is the distance from the leading edge divided by the airfoil's chordlength. For these test conditions the suction peak occurs atapproximately 1% chord. The “chord” of an airfoil is the distancebetween the leading edge and the trailing edge of the airfoil.

FIGS. 2 and 3 illustrate an airfoil 10 that has a venturi 12 with athroat 14, an inlet 16, and a exit 18. The throat of a venturi is thenarrow portion of the venturi, as indicated by reference numeral 14. Theinlet 16 of the venturi is the leading portion of the venturi presentedto the fluid flow ahead of the throat 14. The exit 18 is the portion ofthe venturi that is aft of the throat 14. The fluid (e.g., air) entersthe inlet 16, passes through the constricted throat section 14, andexits through the exit 18. The fluid that exits the throat 14 is at alower pressure than the fluid on the inlet side of the throat. This lowpressure condition can generate increased lift.

The venturi shown in FIGS. 2 and 3 has a throat 14 that extends from2.5% chord to 7.5% chord (i.e., the throat starts at a distance from theleading edge equal to 2.5% of the chord length of the airfoil and endsat 7.5% of the chord length). This venturi configuration results in arelatively small size inlet 16. As a result of the reduced size inlet16, there may be reduced airflow into the venturi.

FIGS. 4 and 5 illustrate an airfoil 10 with a venturi 12 that has athroat 14 that starts at 5.0% chord and extends to 10% chord. A venturiof this shape results in a larger inlet 16, which can allow greaterairflow into the venturi. As can be seen in FIG. 5, neighboring venturiare closely spaced along the surface of the airfoil 10. However, otherspacings can be used in combination with this venturi shape, and othercombinations and variations of the venturi parameters can also be used.

FIGS. 6 and 7 illustrate an airfoil 10 with a venturi 12 that has athroat 14 that starts at 7.5% chord and extends to 12.5% chord. Anairfoil with venturi of the shape results in the throat 14 of theventuri being located relatively far downstream from the leading edge ofthe airfoil.

FIGS. 2-7 illustrate airfoils having venturi with different throat andinlet designs. FIGS. 8-11 illustrate airfoils having venturi withdifferent exit structures. The exit 18 shown in FIGS. 8 and 9 has a“diffuser” profile. Accordingly, the walls of the exit 18 flare awayfrom each other along the length of the airfoil such that the walls ofthe exit 18 are close together near the throat 14 and are further apartnear the end of the exit. The angle “a” between the walls of the exit 18is preferably limited to about 10 degrees in order to reduce the chanceof a flow separation. The exit 18 shown in FIGS. 10 and 11 has a“straight” profile. Accordingly, the walls of the exit 18 maintain thesame spacing along the length of the airfoil. As can be seen, the exit18 has the same wall spacing as the throat 14 along its entire length. Adiffuser shaped exit can increase the velocity through the throat of theventuri leading to increase suction on the aft side of the throat, andthus increased lift. The straight shaped exit can result in lesssuction, but a broader region of low pressure along the surface of theairfoil.

FIGS. 12-14 illustrate airfoils that have venturi of differing “floorprofiles.” The depth of the floor profile is the depth to which theventuri channel is recessed into the airfoil. Referring to FIG. 12, line20 shows the depth profile of a shallow floor venturi and line 22 showsthe depth profile of a deep floor venturi. In addition, as can be seen,profile 20 more closely approximates the original curvature shape of theairfoil 10, whereas profile 22 is deeper in the throat section of theventuri. Lines 20 and 22 represent the depth of the respective venturirelative to the cross-section of airfoil 10. Line 20 corresponds to theventuri 12′ shown in FIG. 14 and line 22 corresponds to the venturi 12″shown in FIG. 13. As can be seen by comparison of FIGS. 13 and 14, thethroat 14′ in FIG. 14 is shallower than the throat 14″ of FIG. 13. Adeep venturi profile can generate a stronger stream wise vortex to helpdelay stall, but generate less flow velocity through the venturi'sthroat (resulting in less suction). A shallow venturi profile can yieldbetter flow and suction in the throat, but weaker vortices. Referring toFIG. 12, both the profiles are shaped so as not to reduce the leadingedge radius 24 beyond a critical minimum radius, which can result in aleading edge stall. In addition, the profiles are shaped to smoothlyexit and transition to the baseline airfoil profile 26 to reduce thechance of flow separation. Accordingly, the profile exits are angled tobe smooth and gradual near the reentry to the baseline airfoil profile.

FIG. 15 shows an airfoil 10 with venturi 12 that are closely spaced.FIG. 16 shows an airfoil 10 with venturi 12 that are widely spaced.Accordingly, the distance 28″ between venturi as shown in FIG. 15 isless than the distance 28′ as shown in FIG. 16. Accordingly, the venturidensity, i.e., the number of venturi per length of airfoil can beadjusted.

FIGS. 17 and 18 illustrate an airfoil having a base shape correspondingto the national advisory committee for aeronautics (NACA) airfoil shapedesignated NACA 0015 was selected as the base airfoil shape. Note thatthe circles on the shown on the airfoil drawings represent rivet holes.The airfoil 110 includes a venturi 112. The venturi 112 are channelsthat are defined between adjacent protrusions 114. The venturi channels112 include a leading portion 116, a middle portion 118, and a trailingportion 120. The walls of the adjacent protrusions 114 are curved towardeach other in the leading portion 216 of each channel 112, which canhave a combination convex concave profile. The walls of protrusions 114are generally parallel with each other in the middle portion 118 of eachchannel 112. The walls of the adjacent protrusions 114 are angled awayfrom each other in the trailing portion 120 of each channel 112. Thewalls of the protrusions 114 in the trailing portion 120 of each channel112 can either be generally linearly angled away from one another orslightly curved away from one another. The leading portion 116 and thetrailing portion 120 of each channel are wider than the middle portion118. The middle portion 118 is substantially longer than the leadingportion 116 and the trailing portion 120. The channel 112 extends alonga majority of the chord length of the airfoil. The channel 112 canextend between about 70% and 95% of the chord length. The walls of theprotrusions can have a rounding radius to smooth the transition, e.g.,the transition from the top wall to a side wall of a protrusion can havea 0.02% radius of rounding. Referring to FIG. 18, the distance between atop surface 122 of the protrusion 114 and the top surface 110 a of theairfoil 110 is greater proximate the leading edge of the airfoil andless proximate the trailing edge of the airfoil. The top surface 122 ofthe protrusion 114 converges with the top surface 110 a proximate thetrailing edge of the airfoil.

FIGS. 19 and 20 show an airfoil 210 with venturi 212. The venturi 212are channels that are defined between adjacent protrusions 214. Theventuri channels 212 include a leading portion 216, a middle portion218, and a trailing portion 220. The walls of the adjacent protrusions214 are curved toward each other in the leading portion 216 of eachchannel 212, which can have a combination convex concave profile. Thewalls of protrusions 214 are generally parallel with each other in themiddle portion 218 of each channel 212. The walls of the adjacentprotrusions 214 are angled away from each other in the trailing portion220 of each channel 212. The walls of the protrusions 214 in thetrailing portion 220 of each channel 212 can either be generallylinearly angled away from one another or slightly curved away from oneanother. The leading portion 216 and the trailing portion 220 of eachchannel are wider than the middle portion 218. The trailing portion 220is substantially longer than the leading portion 216 and the middleportion 118. The channel 212 extends along a majority of the chordlength of the airfoil. The channel 212 can extend between about 70% and95% of the chord length. Referring to FIG. 20, the distance between atop surface 222 of the protrusion 214 and the top surface 210 a of theairfoil 210 is greater proximate the leading edge of the airfoil andless proximate the trailing edge of the airfoil. The top surface 222 ofthe protrusion 214 converges with the top surface 210 a proximate thetrailing edge of the airfoil.

FIGS. 21 and 22 show an airfoil 310 with venturi 312. The venturi 312are channels that are defined between adjacent protrusions 314. Theventuri channels 312 include a leading portion 316, a middle portion318, and a trailing portion 320. The walls of the adjacent protrusions314 are curved toward each other (following a concave curve portion 317and a convex curve portion 319) in the leading portion 316 of eachchannel 312. The concave curve portion 317 is shorter than the convexcurve portion 319. The walls of protrusions 314 are generally parallelwith each other in the middle portion 318 of each channel 312. The wallsof the adjacent protrusions 314 are angled away from each other in thetrailing portion 320 of each channel 312. The walls of the protrusions314 in the trailing portion 320 of each channel 312 can either begenerally linearly angled away from one another or slightly curved awayfrom one another. The leading portion 316 and the trailing portion 320of each channel are wider than the middle portion 318. The trailingportion 320 and the middle portion 318 are about the same length andboth are substantially longer than the leading portion 316. The channel312 extends along a majority of the chord length of the airfoil. Thechannel 312 can extend between about 70% and 95% of the chord length.Referring to FIG. 22, the distance between a top surface 322 of theprotrusion 314 and the top surface 310 a of the airfoil 310 is greaterproximate the leading edge of the airfoil and less proximate thetrailing edge of the airfoil. The top surface 322 of the protrusion 314converges with the top surface 310 a proximate the trailing edge of theairfoil.

FIGS. 23-25 show an airfoil 410 with venturi 412 a on the top surface410 a of the airfoil and a diffuser 412 b on the bottom surface 410 b ofthe airfoil. The venturi 412 a and diffuser 412 b are channels that aredefined between adjacent protrusions 414 a that extend from the topsurface 410 a and extend around the leading edge of the airfoil to thebottom surface 410 b to form protrusions 414 b. The venturi channels 412a on the top surface include a leading portion 416 a, a middle portion418 a, and a trailing portion 420 a. The walls of the adjacentprotrusions 414 a are curved toward each other in the leading portion416 a of each channel 412 a. The walls of protrusions 414 a aregenerally parallel with each other in the middle portion 418 a of eachchannel 412 a. The walls of the adjacent protrusions 414 a are angledaway from each other in the trailing portion 420 a of each channel 412a. The walls of the protrusions 414 a,b in the trailing portion 420 a,bof each channel 412 a,b can either be generally linearly angled awayfrom one another or slightly curved away from one another. The leadingportion 416 a and the trailing portion 420 a of each channel are widerthan the middle portion 418 a. The leading portion 416 a and the middleportion 418 a are about the same length and the trailing portion 420 ais longer than each of the leading portion 416 a and the middle portion418 a. The channel 412 a extends along a majority of the chord length ofthe airfoil. The channel 412 a can extend between about 70% and 95% ofthe chord length.

Referring to FIG. 24, the diffuser 412 b on the bottom surface 410 b hasa different profile than venturi 412 a on the top surface. The diffuserchannels 412 b on the bottom surface include a leading portion 416 b, amiddle portion 418 b, and a trailing portion 420 b. The walls of theadjacent protrusions 414 a are generally parallel with each other in theleading portion 416 b of each channel 412 b. The walls of protrusions414 b are curve away from each other in the middle portion 418 b of eachchannel 412 b. The walls of the adjacent protrusions 414 b are angledaway from each other in the trailing portion 420 b of each channel 412b. The leading portion 416 b is the narrowest part of the channel 412 b.The leading portion 416 b and the middle portion 418 b are about thesame length and the trailing portion 420 b is longer than each of theleading portion 416 b and the middle portion 418 b. The channel 412 bextends along a majority of the chord length of the airfoil. The channel412 b can extend between about 70% and 95% of the chord length.

Referring to FIG. 25, the distance between a top surface 422 a of theprotrusion 414 a and the top surface 410 a of the airfoil 410 is greaterproximate the leading edge of the airfoil and less proximate thetrailing edge of the airfoil. Similarly, the distance between a topsurface 422 b of the protrusion 414 b and the bottom surface 410 b ofthe airfoil 410 is greater proximate the leading edge of the airfoil andless proximate the trailing edge of the airfoil. The top surfaces 422 aand 422 b of the protrusions 414 a and 414 b converge with the topsurface 410 a and bottom surface 410 b, respectively, proximate thetrailing edge of the airfoil

FIGS. 26 and 27 show an airfoil 510 with venturi channels 512 formed byprotrusions 514 that are similar in profile to venturi 312, except thatventuri 512 are shorter than venturi 312 such that the leading, middle,and trailing portion of venturi 512 are all disposed on the airfoilleading portion. The channels 512 extend along a less than half majorityof the chord length of the airfoil. The channels 512 can extend betweenabout 20% and 45% of the chord length.

FIGS. 28-31 show an airfoil 610 that have diffusers 612 that are formedby indentations in the airfoil surface. As can be seen in FIG. 30, thediffusers 612 do not extend beyond the bottom surface 610b of theairfoil 610. The diffusers 612 are narrow near the leading edge of theairfoil 610 and expands along a divergently curving profile toward thetrailing edge. The diffusers 612 extend between about 30% and 60% of thechord length of the airfoil. The walls 613 are generally perpendicularto the surface of the airfoil. The walls of the indentations can have arounding radius to smooth the transition, e.g., the transition from thetop wall to a side wall of an indentation can have a 0.02% radius ofrounding.

A number of examples are provided below that illustrate possibledimensions that can be used to construct airfoils with venturi anddiffusers. The dimensions are provided assuming an airfoil with a nineinch chord and the dimensions are alternatively provided as a percentageof chord length for airfoils having different chord lengths. Thesedimensions are only provided as non-limiting examples and variations ofthese dimensions are contemplated.

EXAMPLE 1

FIG. 32 shows an example of an airfoil with venturi that have a profilethat corresponds to the airfoil illustrated in FIGS. 19 and 20 withexemplary dimensions as follows:

Value Value Refer- for a 9″ as a ence chord percent No. Descriptionairfoil of chord 1A Airfoil chord length 9.000 100.00 1B Distance fromairfoil leading edge to start of 0.062 0.69 venturi Leading Portion 1COverall length of venturi 8.422 93.58 1D Distance from end of venturiTrailing 0.516 5.73 Portion to airfoil trailing edge 1E Length ofventuri Leading Portion 1.839 20.43 1F Length of venturi Middle Portion2.020 22.44 1G Length of venturi Trailing Portion 4.562 50.69 1H Widthof venturi at start of Leading Portion 0.040 0.44 1I Width of venturithroughout Middle Portion 0.527 5.86 1J Width of channel between MiddlePortions 0.675 7.50 of adjacent venturis 1K Center-to-center distancebetween adjacent 1.202 13.36 venturis 1L Width and Height of venturi atTrailing 0.000 0.00 Portion 1M Height of venturi from airfoil surface atthe 0.322 3.58 start of the Leading Portion 1N Height of venturi fromairfoil surface at the 0.200 2.22 start of the Middle Portion 1O Heightof venturi from airfoil surface at the 0.164 1.82 start of the TrailingPortion

EXAMPLE 2

FIG. 33 shows an example of an airfoil with venturi that have a profilethat corresponds to the airfoil illustrated in FIGS. 21 and 22 withexemplary dimensions as follows:

Value Value Refer- for a 9″ as a ence chord percent No. Descriptionairfoil of chord 2A Airfoil chord length 9.000 100.00 2B Distance fromairfoil leading edge to start of 0.062 0.69 venturi Leading Portion 2COverall length of venturi 8.422 93.58 2D Distance from end of venturiTrailing 0.516 5.73 Portion to airfoil trailing edge 2E Length ofventuri Leading Portion 1.091 12.12 2F Length of venturi Middle Portion2.768 30.76 2G Length of venturi Trailing Portion 4.562 50.69 2H Widthof venturi at start of Leading Portion 0.040 0.44 2I Width of venturithroughout Middle Portion 0.527 5.86 2J Width of channel between MiddlePortions 1.125 12.50 of adjacent venturis 2K Center-to-center distancebetween adjacent 1.652 18.36 venturis 2L Width and Height of venturi atTrailing 0.000 0.00 Portion 2M Height of venturi from airfoil surface atthe 0.322 3.58 start of the Leading Portion 2N Height of venturi fromairfoil surface at the 0.233 2.59 start of the Middle Portion 2O Heightof venturi from airfoil surface at the 0.164 1.82 start of the TrailingPortion

EXAMPLE 3

FIG. 34 shows an example of an airfoil with venturi that have a profilethat corresponds to the airfoil illustrated in FIGS. 19 and 20 withsimilar dimensions to Example 1, except that the distance betweenadjacent venturi (Ref No. K) is varied, as follows:

Value Value Refer- for a 9″ as a ence chord percent No. Descriptionairfoil of chord 3A Airfoil chord length 9.000 100.00 3B Distance fromairfoil leading edge to start of 0.062 0.69 venturi Leading Portion 3COverall length of venturi 8.422 93.58 3D Distance from end of venturiTrailing 0.516 5.73 Portion to airfoil trailing edge 3E Length ofventuri Leading Portion 1.839 20.43 3F Length of venturi Middle Portion2.020 22.44 3G Length of venturi Trailing Portion 4.562 50.69 3H Widthof venturi at start of Leading Portion 0.040 0.44 3I Width of venturithroughout Middle Portion 0.527 5.86 3J Width of channel between MiddlePortions 1.125 12.50 of adjacent venturis 3K Center-to-center distancebetween adjacent 1.652 18.36 venturis 3L Width of venturi at end ofTrailing Portion 0.000 0.00 3M Height of venturi from airfoil surface atthe 0.322 3.58 start of the Leading Portion 3N Height of venturi fromairfoil surface at the 0.200 2.22 start of the Middle Portion 3O Heightof venturi from airfoil surface at the 0.164 1.82 start of the TrailingPortion

EXAMPLE 4

FIG. 35 shows an example of an airfoil with venturi that have a profilethat corresponds to the airfoil illustrated in FIGS. 26 and 27 withexemplary dimensions as follows:

Value Value Refer- for a 9″ as a ence chord percent No. Descriptionairfoil of chord 4A Airfoil chord length 9.000 100.00 4B Distance fromairfoil leading edge to start of 0.062 0.69 venturi Leading Portion 4COverall length of venturi 2.970 33.00 4D Distance from end of venturiTrailing 5.968 66.31 Portion to airfoil trailing edge 4E Length ofventuri Leading Portion 0.613 6.81 4F Length of venturi Middle Portion0.449 4.99 4G Length of venturi Trailing Portion 1.908 21.20 4H Width ofventuri at start of Leading Portion 0.040 0.44 4I Width of venturithroughout Middle Portion 0.527 5.86 4J Width of channel between MiddlePortions 1.125 12.50 of adjacent venturis 4K Center-to-center distancebetween adjacent 1.652 18.36 venturis 4L Width and Height of venturi atTrailing 0.000 0.00 Portion 4M Height of venturi from airfoil surface atthe 0.283 3.14 start of the Leading Portion 4N Height of venturi fromairfoil surface at the 0.196 2.18 start of the Middle Portion 4O Heightof venturi from airfoil surface at the 0.150 1.67 start of the TrailingPortion

EXAMPLE 5

FIG. 36 shows an example of an airfoil with venturi that have a profilethat corresponds to the airfoil illustrated in FIGS. 17 and 18 withexemplary dimensions as follows:

Value Value Refer- for a 9″ as a ence chord percent No. Descriptionairfoil of chord 5A Airfoil chord length 9.000 100.00 5B Distance fromairfoil leading edge to start of 0.062 0.69 venturi Leading Portion 5COverall length of venturi 8.364 92.93 5D Distance from end of venturiTrailing 0.574 6.38 Portion to airfoil trailing edge 5E Length ofventuri Leading Portion 1.839 20.43 5F Length of venturi Middle Portion5.597 62.19 5G Length of venturi Trailing Portion 0.928 10.31 5H Widthof venturi at start of Leading Portion 0.040 0.44 5I Width of venturithroughout Middle Portion 0.527 5.86 5J Width of channel between MiddlePortions 1.125 12.50 of adjacent venturis 5K Center-to-center distancebetween adjacent 1.652 18.36 venturis 5L Width of venturi at end ofTrailing Portion 0.040 0.44 5M Height of venturi from airfoil surface atthe 0.322 3.58 start of the Leading Portion 5N Height of venturi fromairfoil surface at the 0.200 2.22 start of the Middle Portion 5O Heightof venturi from airfoil surface at the 0.092 1.02 start of the TrailingPortion 5P Height of venturi from airfoil surface at the 0.031 0.34 endof the Trailing Portion

EXAMPLE 6

FIGS. 37 and 38 show an example of an airfoil with venturi that have aprofile that corresponds to the airfoil illustrated in FIGS. 23-25 withexemplary dimensions as follows:

Value Value Refer- for a 9″ as a ence chord percent No. Descriptionairfoil of chord 6A Airfoil chord length 9.000 100.00 6B Distance fromleading edge of venturi to 0.400 4.44 leading edge of airfoil 6C Lengthof lower venturi Trailing Portion 7.972 88.58 6D Distance from end ofventuri Trailing 0.574 6.38 Portion to airfoil trailing edge 6E Lengthof upper venturi Leading Portion 2.513 27.92 6F Length of upper venturiMiddle Portion 1.786 19.84 6G Length of upper venturi Trailing Portion4.527 50.30 6H Width of venturi at leading edge 1.155 12.83 6I Width ofventuri throughout Middle Portion 1.798 19.98 6J Width of channelbetween Middle Portions 1.506 16.73 of adjacent venturis 6KCenter-to-center distance between adjacent 3.304 36.71 venturis 6L Widthof venturi at end of Trailing Portion 0.000 0.00 6M Height of venturifrom airfoil surface at the 0.319 3.54 start of the lower TrailingPortion 6N Height of venturi from airfoil surface at the 0.209 2.32start of the upper Middle Portion 6O Height of venturi from airfoilsurface at the 0.196 2.18 start of the upper Trailing Portion 6P Lengthof lower venturi Leading Portion 0.854 9.49

EXAMPLE 7

FIG. 39 shows an example of an airfoil with diffusers that have aprofile that corresponds to the airfoil illustrated in FIGS. 28-31 withexemplary dimensions as follows:

Value Value Refer- for a 9″ as a ence chord percent No. Descriptionairfoil of chord 7A Airfoil chord length 9.000 100.00 7B Distance fromairfoil leading edge to start of 0.362 4.02 cavity 7C Length of cavity4.438 49.31 7D Distance from end of cavity to airfoil trailing 4.20046.67 edge 7E Width of cavity at exit 2.642 29.36 7F Width of cavity atentrance 1.352 15.02 7G Distance from airfoil leading edge 1.000 11.117H Distance from airfoil leading edge 2.000 22.22 7I Distance fromairfoil leading edge 3.000 33.33 7J Depth of cavity 1.0 inch fromairfoil leading 0.080 0.89 edge 7K Depth of cavity 2.0 inches fromairfoil 0.109 1.21 leading edge 7L Depth of cavity 3.0 inches fromairfoil 0.079 0.88 leading edge Center-to-center spacing betweencavities 2.642 29.36

While the invention has been described in connection with a certainembodiment and variations thereof, the invention is not limited to thedescribed embodiment and variations but rather is more broadly definedby the recitations in the claims below and equivalents thereof.

What is claimed is:
 1. An airfoil for a vehicle, comprising: a topsurface extending between a leading edge and a trailing edge on a topside of the airfoil and defining a chord length therebetween; a bottomsurface extending between the leading edge and the trailing edge on abottom side of the airfoil; a plurality of protrusions on the topsurface of the air foil, wherein two adjacent protrusions define achannel therebetween that extends in the direction of the chord length;wherein each channel has a leading portion, a middle portion, and atrailing portion, the channel being sized and shaped such that theleading portion and the trailing portion are wider than the middleportion.
 2. An airfoil of claim 1, wherein each channel extends along amajority of the top surface in the direction of the chord length.
 3. Anairfoil of claim 1, wherein the length of the leading portion of eachchannel is shorter than the middle portion in the direction of the chordlength.
 4. An airfoil of claim 3, wherein the length of the trailingportion of each channel is longer than the middle portion in thedirection of the chord length.
 5. An airfoil of claim 1, wherein eachchannel extends along less than half of the top surface in the directionof the chord length.
 6. An airfoil of claim 1, wherein the walls ofadjacent protrusions converge along a curved trajectory to define theleading portion of each channel.
 7. An airfoil of claim 1, wherein thewalls of adjacent protrusions diverge along a generally lineartrajectory to define the trailing portion of each channel.
 8. An airfoilof claim 1, wherein the walls of adjacent protrusions extend generallyparallel to each other to define the middle portion of each channel. 9.An airfoil of claim 1, wherein distance between a top surface of eachprotrusion and the top surface of the airfoil defines a depth of eachchannel, and the depth of each channel is greater in the leading portionthan the middle portion and the trailing portion.
 10. An airfoil ofclaim 1, wherein each protrusion extends around the leading edge to thebottom surface of the airfoil such that adjacent protrusions formchannels on the bottom surface of the airfoil.
 11. An airfoil for avehicle, comprising: a top surface extending between a leading edge anda trailing edge on a top side of the airfoil and defining a chord lengththerebetween; a bottom surface extending between the leading edge andthe trailing edge on a bottom side of the airfoil; a plurality ofindentations on the bottom surface of the air foil each defining achannel, wherein each indentation has a leading portion and a trailingportion, the channel being sized and shaped such that the trailingportion is wider than the leading portion.